Henkel, melamine production

Melamine resins were introduced about ten years after the Beetle molding compound. They were very similar to those based on urea but had superior quaHties. Henkel in Germany was issued a patent for a melamine resin in 1936 (7). Melamine resins rapidly supplanted urea resins and were soon used in molding, laminating, and bonding formulations, as well as for textile and paper treatments. The remarkable stabiHty of the symmetrical triazine ring made these products resistant to chemical change once the resin had been cured to the insoluble, cross-linked state. 

In 1935 Henkel patented the production of resins based on melamine. Today these resins are important in the manufacture of decorative laminates and in tableware. 

Melamine (I,3,5-triamino-2,4,6-triazine) was first prepared by Liebig in 1835. For a hundred years the material remained no more than a laboratory curiosity until Henkel patented the production of resins by condensation with formaldehyde. Today large quantities of melamine-formaldehyde resins are used in the manufacture of moulding compositions, laminates, adhesives, surface coatings and other applications. Although in many respects superior in properties to the urea-based resins they are also significantly more expensive. 

The production of MF was first patented in 1935 by Henkel (Brydson, 1999). Today, MF polymers have commercial applications in decorative laminates for chipboard (a low cost substitute for solid wood) and unbreakable tableware. During synthesis, an excess of formaldehyde is heated with melamine at 80°G in alkaline conditions to produce an aqueous, syrup-like prepolymer. The prepolymer contains melamine-formaldehyde in a molar ratio of 1 2 (Figure 3.8). It is compounded with fillers, pigments, lubricants, stabilizers and sometimes accelerators, dried and milled to powder. Heating the powder to mould it at 145-165°C and 30-60 MPa produces a solid, thermosetting network. 

Melamine was first isolated by Liebig in 1834 from the mixture obtained by heating ammonium thiocyanate. A technically feasible route to melamine was developed in 1935 by Ciba AG (Switzerland) and at the same time Henkel patented the production of resins from melamine and formaldehyde. In general, melamine-formaldehyde polymers resemble urea-formaldehyde pol)miers but they have improved resistance to heat and water. The two materials have therefore found application in similar areas, melamine-formaldehyde resins now being widely used in the production of moulding powders, laminates, adhesives, surface coatings and textile finishes. 

Melamine reacts with several other aldehydes as well as with alcohols to give etherified products. Most other aldehydes give resinous products that have not been fully characterized. Rudelburgher reacted melamine (2 moles) with glucose (1.0 mole) to obtain a derivative melting at 218°C [69]. The synthesis of a curable melamine-acetaldehyde resin was reported by Henkel Co. [70]. The reaction of melamine with aldehydes such as benzaldehyde, cinnamaldehyde, hexahydrobenzaldehyde, terephthalaldehyde, and acrolein have been reported [71]. 

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